1. Field of the Invention
The present invention relates to a technique of trimming for a semiconductor integrated circuit, and in particular, it relates to a technique suitable for holding trimming information for use in an oscillation circuit that generates a clock signal.
2. Description of the Related Art
Well-known semiconductor integrated circuits such as microcomputers synthesized by clock pulses generate clock signals with an oscillation circuit having a crystal oscillator in the semiconductor integrated circuit not on the outside.
Some of these semiconductor integrated circuits have a trimming circuit that prevents variations in oscillation frequency generated by the oscillation circuit due to the variations of the process, fluctuations in supply voltage, or temperature changes (e.g., U.S. application Ser. No. 11/188873).
In this case, the trimming circuit includes a trimming fuse circuit capable of storing control information generated by a logic circuit that generates control information for matching the frequency of an external clock signal generated externally with that of an internal clock signal.
The trimming fuse circuit includes an information-writing blow fuse that allows writing of control information depending on whether to be blown; and a reference blow fuse equivalent to the unblown condition of the information-writing blow fuse. The trimming fuse circuit compares a current flowing in the information-writing blow fuse to a current flowing in the reference blow fuse to determine whether the information-writing blow fuse has been blown, thereby obtaining trimming information.
The inventor has found that the above-described trimming technique for the semiconductor integrated circuit has the following problems.
To trim the oscillation frequency of a clock signal with high accuracy, trimming information of multiple bits is required. For 8-bit trimming information, for example, eight trimming fuse circuits are required.
Correspondingly, the numbers of the information-writing blow fuses and the reference blow fuses also increase, resulting in an increase in the chip area occupied by the trimming fuse circuit. This may inhibit size reduction of a semiconductor integrated circuit.